1. Field of Invention
The invention concerns a needle roll for perforation or pickup of material pieces or webs as described herein, as well as a method for perforation or pickup of material pieces or webs that employs the aforementioned needle roll.
2. Description of the Prior Art
Needle rolls are often used to perforate material webs, for example, paper webs, from which tube pieces and ultimately sacks or bags are produced. Such perforations are often produced, in order to be able to vent such sacks after filling. The same also applies for bags, in which, say, bread is packed. The perforations so produced serve here to release moisture. A device including such needle rolls is described in EP 0 776 741 A1. Printed products are often provided with perforations, as is disclosed in U.S. Pat. No. 4,055,101.
However, needle rolls are also used to pick up material pieces, when a separate material piece is to be removed from the material flow. One application is the removal of so-called flaps, i.e., material pieces, during production of paper bags from web-like paper.
All the mentioned needle rolls are mounted to rotate in the machine frame or other components that are kept fixed during operation (for simplicity, only “machine frame” will be at issue below). The peripheral speed in some applications is the same as the transport speed in the material webs or pieces and in other applications, the peripheral speed of the needle rolls can differ from the transport speed. The needle rolls can have different variants. All variants have the common feature, however, of a needle roll body that can roll on the material web with its outside periphery.
Regardless of the application, the needles for piercing the material piece or material web protrude beyond the outer surface of the needle roll body.
A commonly occurring problem in needle rolls is loosening of the material piece or web after puncturing. For example, during perforation of webs, the needles and the web should loosen from each other again, without the needles having an effect on web tension. During removal of a material piece from the material flow, the problem often occurs that this material piece, after pickup by the needle roll, must also be removed from it again, so that the needle roll can pick up a new material piece again during the next revolution.